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A098685 Numbers n such that pi(n) = sigma(d_1)*sigma(d_2)*...*sigma(d_k) where d_1 d_2 ... d_k is the decimal expansion of n. 4
15, 155, 252, 916, 1189, 12654, 55293, 177554, 418634, 753248, 885193, 18252678, 18252687, 18469156, 18469165, 19882616, 19882623, 41867246, 73526936, 73526957, 233843449, 244895519, 2345784285, 2399877831, 4273447776, 29891923496, 42649454852, 728781494646 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n) must necessarily be a zeroless number. - Chai Wah Wu, Mar 04 2019

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..34

EXAMPLE

885193 is in the sequence because pi(885193) = sigma(8)*sigma(8)*sigma(5)*sigma(1)*sigma(9)*sigma(3).

MATHEMATICA

Do[d=IntegerDigits[n]; k=Length[d]; If[ !MemberQ[d, 0]&&PrimePi[n]== Product[DivisorSigma[1, d[[j]]], {j, k}], Print[n]], {n, 10000000}]

CROSSREFS

Cf. A000203, A000720, A052382, A098686, A098683, A098684.

Sequence in context: A017389 A278803 A157380 * A223995 A323971 A006096

Adjacent sequences:  A098682 A098683 A098684 * A098686 A098687 A098688

KEYWORD

base,nonn

AUTHOR

Farideh Firoozbakht, Sep 24 2004

EXTENSIONS

a(12)-a(25) from Donovan Johnson, Jun 18 2009

a(26)-a(28) from Chai Wah Wu, Mar 04 2019

STATUS

approved

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Last modified April 19 01:29 EDT 2019. Contains 322237 sequences. (Running on oeis4.)